X-ray tube



June 12, Gb HOLST ET AL 1,962,275

X-RAY TUBE Filed June 26, 1930 L( i J d# l l g Patented June 12., 1934 UNITED STATES PATENT OFFICE.

X-RAY TUBE Application June 26, 1930, Serial No. 464,067 In the Netherlands August 2, 1929 11 Claims.

` This invention relates to improvements in or modification of the X-ray tube as claimed in patent application, Ser. No. 186,522, filed April 25,

1927 now U. S. Patent No. 1,893,759.

The X-ray tube according to the prior application has an anticathode whichis caused to rotate during the operation as it is integral with the armature of an electric motor whose stator is arranged outside the tube. By this construction it isrendered possible to increase the load of the tube to a considerable extent, since the continuous displacement of the focal spot over the surface of the anticathode materially reduces the risk of burning` the latter.

The present invention relates to an improvement of the X-ray tube referred to above, whereby it is rendered particularly suitable for the application of high loads.

When an X-ray tube is loaded for a short time, a higher load may, of coiu'se, be applied than when the tube is loaded for a longer period. After a high load of short duration one must wait some time until the anticathode is sufficiently cooled, before beginning with 'a new load period. In addition to radiation of the heat, this cooling is also effected by conduction of the heat by the members to which the anticathode is xed and which in their turn dissipate the heat by radiation or convection.

Since a tube having a rotatory anticathode may be loaded to a higher extent, a greater quantity of heat will be produced therein than in a tube oi the same size having a stationary anticathode which is loaded during a corresponding period. Due to this the time required for the cooling becomes longer. This invention has for its object to shorten this coooling period.

According to the invention in an X-ray tube having a rotatory anticathode as claimed in the above-mentioned patent application a displacement of the anticathode is possible relative to a member which when in thermal contact with the anticathode, carries olf the heat produced therein in such a manner that the thermal contact may be kept broken during the rotation and maintained closed when the anticathode is at rest.

Of course the heat conducting contact between the rotatcry anticathode and its supporting members must necessarily remain relatively imperfect during rotation of the anticathode, since any improvement of this contact is attended with an increase of the friction. This drawback is not encountered, however, when the anticathode is at rest. The present invention renders it possible td reduce the friction as much as necessary during (Cl. Z50-35) the rotation while at the same time a good heat conducting contact between the movable and a stationary member may be established when the anticathode is at rest.

The displacement of the anticathode relative to the member carrying oli the heat may be brought about in various ways, for example, by gravity or by means of a magnetic force. This may be effected by providing that the member may be moved towards and away from the anticathode. A very simple solution is obtained by providing that the anticathode has some play in an axial direction so that it may be displaced in this direction and may be brought into contact with or moved away from a surface carrying off the heat.

This may be effected, for example, by placing the tube upside down. In this case the anticathode, due to its weight, will bear in one position on the member carrying off the heat while in the opposite position of the tube the thermal contact surfaces of the anticathode and oi this member will move away from each other, so that the anticathode may rotate without any friction being produced between these surfaces.

In order to bring about such a relative displacement, itis advantageous to use the magnetic force of the stator of the motor. For this purpose, the position of the stator relative to the rotor may be so chosen, that the stator' exerts a force in an axial direction on the rotor, said force counteracting another force (gravity, elastic force) acting on the antcathode.

In order to ensure a rapid cooling it is advisable to lodge the greater part of member carrying off the heat within the hollow anticathode body.

The invention will be more clearly understood by reference to the accompanying drawing representing, by way of example, two einbodiments thereof.

Figure 1 shows part of an X-ray tube in which the force of the magnetic field exerted by the stator on the anticathode has a component counteracting the force of a spring.

Fig. 2 shows a similar arrangement in which the field of the stator counteracts the action of gravity.

In Fig. 1 the wall of the X-ray tube, which is partly made of metal, is denoted by l. A vitreous wall portion 2 is inserted between two metal wall portions 3 and 4 at the middle of the tube and the two portions are together electrically connected through the vitreous wall portion.

Around the tube a magnet system 5 is disposed, on which windings 6 are provided. When the latter are connected to a suitable source of alternating current, they set up a rotary eld, which causes the anticathode 8 of the X-ray tube to rotate. The anticathode consists essentially of two parts, viz. a copper part 9 and an iron part 11. The copper part has a conical end surface in which an annular piece 10 made of tungsten is embedded at the point where the cathode rays strike the anticathode, i. e. at the point where the focal spot is formed thereon. The cathode of the tube is denoted by 7. The iron part is ring shaped and screwed into the upper end of the copper part. Between this iron ring 11 and the copper part 9 a cylinder 14 is clamped which may likewise consist of copper.

The ring 11 together with the copper shell mounted thereon constitute the rotor of an induction motor. The rotor is provided with bearings 12 and 13. In order to be able to mount these bearings they are constituted by two or more parts, which are held together by the iron ring 11 and the copper cylinder 14 respectively. I'hese bearings bear on a hollow spindle 15 and preferably consist of a material which is less hard and has a greater coefficient of expansion than the material over which they move. 'I'hey may be made, for example, of a copper-graphite alloy, While the spindle 15 may consist of an alloy of iron and chromium, so that it is possible to seal the edge 16 of this spindle to the glass portion of the X-ray tube. A head 17 at the end of the spindle 15 constitutes the member carrying off the heat from the anode and has a conical end surface 18 which contacts with a surface of the anticathode portion 9 which closely flts thereto.

The head 17 has a cavity into which a cooling liquid may be introduced by means of a tube 19. 'This liquid may flow back through the space between the inner wall of the spindle and the Outer wall of the tube 19, so that a. continuous circulation is maintained. On the spindle 15 a tube 20 is mounted serving for carrying 01T the liquid and for conducting the current to the anticathode.

Within the cylinder 14 a helical spring 21 is provided which acts on the one hand on the ring 1l and on the other hand on the bearing 13 which in its turn acts upon the annular guide surface 22 of the spindle head 17. It should be noted that the bearing 13 is not rigidly secured to the anticathode, but may slightly move in an axial direction relatively to the cylinder 14. Upon this axial displacement, however, it soon abuts `against a shoulder 23 so that only a slight displacement is possible. The bearing 13 is prevented from rotating relatively to the cylinder 14 by a pin 24.

Owing to the action of the spring 21, the ring 11 and consequently the whole anticathode with the cylinder 14 are raised, so that the inner conical surface of the copper portion 9 of the anticathode bears on the end surface 18 of the member 17 carrying-off the heat.

When the current passing through the magnet windings is switched on, the magnetic field produced thereby exerts a downward force on the ring 11, Which is disposed asymmetrically relatively thereto, said force being greater than the elastic force. Due to this the anticathode is displaced in an axial direction relatively to the spindle 15, but the bearing 13, engaging the guidesurface 22 remains in position. 'Ihe shoulder 23 now bears on the edge of the bearing 13. No

extra friction is produced thereby, since the cylinder 14 and the bearing 13 do not rotate relatively to one another.

Due to the displacement of the anticathode the latter no longer has Contact with the surface 18, so that the friction caused by this contact, no longer exists. Consequently the anticathode may freely rotate with very little friction.

When the current in the winding 6 is switched off upon expiration of the load period, the magnetic force ceases and the anticathode body is lifted by the spring, thus bringing the end surface 18 again into contact with the anticathode which is now at rest. In this position the heat produced by the load at the surface of the anticathode will be rapidly carried-off through the copper portion 9 due to the heat conducting contact between the anticathode and the member 17 which is internally cooled by means of a. liquid, so that the temperature of the anticathode after a very short time will have sufficiently decreased for applying another load.

By rendering the magnetic force of the field and the elastic force sufficiently great, the influence of the weight of the anticathode may be reduced, so that the arrangement functions in any desired position of the tube.

If, however, the tube is to be used in only one position, then a construction as is diagrammatically illustrated in 2 may be used. ThisV iigure shows the middle portion of a cylindrical X-ray tube in which the anticathode 30, due to its weight, bears on the spindle head 31. Owing to the magnetic field of the stator 5 the iron ring 32 is lifted, so that the contact between the anticathode 30 and the forward surface of the head 31 is broken, due to which the anticathode may rotate in the nel-cl. 0n switching off the current in the magnet winding the anticathode body, due to its weight, falls back on the head 31 which carries off the heat.

In the construction shown in Fig. 2 the displacement may be brought about by placing the tube upside down. In one position of tube, as shown, the anticathode is brought into contact with the cooling member by gravity, when the tube is turned into the other position the heat conducting contact is broken thereby, while at the same time the friction between the thermal contact surfaces is suppressed.

The wall of the X-ray tube shown in Fig. 2 has a portion formed by a metal cylinder 33 made, for example, of chrome-iron. whose rim is sealed to a glass portion 34 of the tube. This cylinder 33 has a window 35 for the passage of a beam of X-rays emitted by the focal spot of the antcathode and this cylinder, as well as the metal wall portions 3 and 4, shown in Figure l, may be connected to earth during the operation of the tube.

A conducting coating 36 which is provided on the inner side of the vitreous wall portion of the tube and which extends beyond the magnet system (not represented) constitutes from an elec trical point of View, a continuation of the metal cylinder 33 and prevents the production of an electric field in the air-gap of the motor located outside the X-ray tube. Consequently the tube may be closely surrounded by the magnet system, as is shown in Fig. 1.

What we claim is:

1. An X-ray tube comprising an envelope, a cathode and a rotatable anti-cathode therein, cooling means for the anti-cathode, means to engage said anti-cathode with said cooling means when the anti-cathode is at rest and means to disengage said anti-cathode from said cooling means and to impart rotative motion to the anticathode.

2. An X-ray tube comprising an envelope, a cathode and a rotatable anti-cathode therein, cooling means for the anti-cathode, said anticathode being normally in contact with said cooling means, and common means to disengage said anti-cathode from said cooling means and to rotate it when such disengagement has been effected.

3. An X-ray tube comprising an envelope, a cathode and a rotatable anti-cathode therein, cooling means for the anti-cathode, resilient means tending to maintain said anti-cathode in Contact with said cooling means and magnetic means for effecting disengagement of said anticathode from said cooling means.

4. An X-ray tube comprising an enclosing envelope, a cathode and an anode mounted therein, the anode having a rotatively mounted portion disposed opposite to the cathode, a stationary body of high heat conductivity adapted to engage on a substantial area of the rotatable portion of the anode, means to produce a relative displacement between the anode and said body to obviate such engagement and to rotate the movable part of the anode when it is disengaged from the body.

5. An X-ray tube comprising a receptacle, a cathode, an anode and a heat-conductive body, the anode comprising a target and a movable portion to carry said target, said movable portion adapted to engage with a substantial portion of said heat-conductive body, said anode portion being capable of lateral displacement with respect to the heat-conductive body and means to produce rotation of said movable portion when it is in a displaced position.

6. An X-ray tube comprising a receptacle, a cathode, an anode, and a heat-conductive body disposed within said anode, said anode having a rotatable portion shiftably mounted in said receptacle and adapted to occupy two positions in at least one of Which it is held by gravity, said heat-conductive body being in one of the said positions in good thermal contact with a considerable portion of the surface of said rotatable portion and means for producing a rotation of said rotatable portion when the rotatable portion occupies the other of said positions.

7. An X-ray tube comprising a receptacle, an anode and a cathode therein, the anode having a movable portion shiftably and rotatably mounted in said receptacle, said portion comprising a ferromagnetic body, a heat-conductive body secured to the wall of the receptacle, said movable portion being adapted to be shifted into two extreme positions and in one of said positions engaging said heat-conductive body, and means for producing an external magnetic field acting on said ferromagnetic body so as to shift the movable portion in one of its two positions and to rotate the movable portion when it is out of engagement with the heat-conductive body.

8. An X-ray tube comprising a receptacle, an anode and a cathode therein, the anode comprising a movable portion, and a heat-conductive body secured to the wall of the receptacle and having a portion forming a supporting member for said movable portion, said movable portion being mounted for translation and rotation on said supporting member and adapted to occupy two positions relative to said body in one of said positions engaging said body, and in the other position being free to rotate about said supporting member, means mounted outside the tube for moving said movable portion, said means comprising a magnetic stator producing a rotary magnetic field to move the movable portion into the position in which it is free to rotate and to impart rotation thereto When it is in such position.

9. An X-ray tube comprising a receptacle, a cathode and an anode therein, said anode comprising a movably mounted hollow body, cooling and supporting means about which said hollow body can rotate, said movable body being slidable for a small distance on said means to occupy two extreme positions, resilient means urging said body to one position, said cooling and supporting means being in frictional contact with a substantial portion of the inner surface of the movable body when the latter assumes one extreme position and means for temporarily moving said movable body into the other extreme position to reduce such frictional Contact, said means comprising an external magnetic stator producing a rotary magnetic eld, and having a component in the direction of the shaft to counteract the force of the resilient means and to move the movable body into the extreme position in which it may freely rotate, and means to limit the sliding movement of the movable body.

10. An X-ray tube comprising a cylindrical receptacle, a cathode and an anode mounted therein, said anode comprising a hollow movable body of circular cross-section and mounted concentrically within the receptacle, a target located in said body on its surface opposing the cathode, cooling and supporting means for said anode extending inside of said hollow body, means to circulate a cooling fluid therethrough, said anode being rotatable on said cooling and supporting means and said movable body being adapted to engage a considerable portion of the surface of said cooling and supporting means to facilitate conduction of heat from the anode, said movable body being further movable in an axial direction to a position in which it is free to rotate, and means for imparting rotation to said body when in the latter position.

l1. An X-ray tube comprising an envelope, a cathode and a rotatable anti-cathode therein, cooling means for the anti-cathode, said anticathode being slidably supported with respect to said cooling means to permit the same to move into and out of engagement with said cooling means under the iniiuence of gravity when the tube is tilted, and means to rotate the anticathode when disengaged from said cooling means.

GILLES HOLST. ALBERT BOUWERS. 

